I would think the manual transmission would exert more torque forces on the halfshafts than the fluid coupled automatic. Manual transmissions have always found the weakness of a driveline. The desire to have all the power delivered on acceleration is the main reason people choose manuals. I, on the other hand, realised early in my automotive experience that I was not Ronnie Sox. The reason many early drag racers chose autos was due to less breakage and consistency.